1. Field of the Invention
The present invention relates to a recording medium feeding mechanism. More particularly, the invention relates to a highly reliable recording medium feeding mechanism which can be easily manufactured and assembled, and a recording apparatus using such a feeding mechanism.
2. Related Background Art
Apparatuses for recording, reading, and others are able to feed a sheet for a given recording or reading in synchronism with the feeding, and this sheet feeding is generally performed by rotating a rubber roller.
As a typical structure of the foregoing sheet feed roller, a resilient member made of rubber or the like is fixed to a metal shaft by thermal bonding or, as shown in FIG. 20, the foregoing resilient member 80 is fixed to a holder 82 for a metal shaft 81 to constitute a roller. Also, a gear is separately prepared for transmitting rotational driving force to the foregoing metal shaft and is fixed to the metal shaft for the conventional type roller.
Of the above-mentioned conventional examples, the method wherein the resilient member is fixed to the holder for the metal shaft is more widely used than the one to thermally bond the resilient member to the metal shaft. In this case, however, the resilient member 80 must be inserted into the holder 82 by tight fitting in its assembly and then, in order not to allow the resilient member 80 to move in the thrust direction of the metal shaft 81, the resilient member 80 is held by protrusions 82a of the holder 82.
The foregoing resilient member 80 is inserted from the end portion of the shaft 81, but if this end portion of the shaft is formed thick, the resilient member should be expanded while being inserted. Thus, the operational efficiency is lowered. On the other hand, if the foregoing shaft 81 is formed thin, the bending strength of the shaft 81 itself becomes weak although the insertion of the resilient member 80 is easier. However, as the driving force transmission gear is integrally structured, this can hardly be practicable particularly when the shaft 81 is made of resin.
Now, to examine the diameter of the shaft 81, the shaft strength, and the inner diameter of the resilient member, the relationship therebetween can be worked out to be a curve represented in FIG. 21. In FIG. 21, if, for example, the allowable deflection for the shaft is given as 0.08 mm, it is necessary to establish the shaft diameter more than 5.9 mm. However, unless the inner diameter of the resilient member is more than 5.9 mm+.alpha.(.alpha.&gt;0), that is, a value having a slight margin added to 5.9 mm, it is impossible to improve the foregoing operational efficiency. Meanwhile, there is no flexibility in determining the diameter of the resilient member due to the design restrictions (the target amount of sheet feeding and the rotational amount of the shaft, for example). This often hinders the establishment of optimal conditions.
Also, when the foregoing resilient member 80 is inserted between the protrusions 82a, it is necessary to expand the resilient member 80 to negotiate these protrusions 82a. From this point of view, there is also a problem in making the assembling efficiency high among others.